using System;
        using System.Collections.Generic;
        using System.Linq;

        public class Test
        {
                public static void Main()
                {
                        List<string> validatedStrings = new List<string>();
                        List<string> subjectStrings = new List<string>()
                        {
                                "con", "cot", "eon", "net", "not", "one", "ten", "toe", "ton",
                                        "cent", "cone", "conn", "cote", "neon", "none", "note", "once", "tone",
                                        "cento", "conte", "nonce", "nonet", "oncet", "tenon", "tonne",
                                        "nocent","concent", "connect"
                        }; //got a more longer wordlist
                
                        string startswithString = "co";
                        string endswithString = "et";
                
                        foreach(var z in subjectStrings)
                        {
                            bool valid = false;
                            foreach(var a in getCombinations(startswithString))
                            {
                                foreach(var b in getCombinations(endswithString))
                                {
                                    if(z.StartsWith(a) && !z.EndsWith(b))
                                    {
                                            valid = true;
                                            break;
                                    }
                                }
                                if(valid)
                                {
                                    break;
                                }
                            }
                            if(valid)
                            {
                                validatedStrings.Add(z);
                            }
                        }

                        foreach(var a in validatedStrings)
                        {
                                Console.WriteLine(a);
                        }
                        Console.WriteLine("\nDone");
                }

            
                static List<string> getCombinations(string s)
                {
                        //Code that calculates combinations
                        return Permutations.Permutate(s);
                }
        }

        public class Permutations
        {
                private static List<List<string>> allCombinations;
                
                private static void CalculateCombinations(string word, List<string> temp)
                {
                        if (temp.Count == word.Length)
                        {
                                List<string> clone = temp.ToList();
                                if (clone.Distinct().Count() == clone.Count)
                                {
                                        allCombinations.Add(clone);
                                }
                                return;
                        }

                        for (int i = 0; i < word.Length; i++)
                        {
                                temp.Add(word[i].ToString());
                                CalculateCombinations(word, temp);
                                temp.RemoveAt(temp.Count - 1);
                        }
                }
                
                public static List<string> Permutate(string str)
                {
                        allCombinations = new List<List<string>>();
                        CalculateCombinations(str, new List<string>());
                        List<string> combinations = new List<string>();
                        foreach(var a in allCombinations)
                        {
                                string c = "";
                                foreach(var b in a)
                                {
                                        c+=b;
                                }
                                combinations.Add(c);
                        }
                        return combinations;
                }
        }